HR: 1340h
AN: H53F-1475    [Abstracts]
TI: Gas Diffusivity And Air Permeability In Sandy Soils: Effect Of Particle Size, Compaction And Sample Scale
AU: * Hamamoto, S
EM: s07de004@mail.saitama-u.ac.jp
AF: Department of Civil & Environmental Engineering, Graduate School of Science & Engineering, Saitama University, 255 Shimo-Okubo, Saitama, 338-8570, Japan
AU: Kawamoto, K
EM: kawamoto@post.saitama-u.ac.jp
AF: Department of Civil & Environmental Engineering, Graduate School of Science & Engineering, Saitama University, 255 Shimo-Okubo, Saitama, 338-8570, Japan
AU: Moldrup, P
EM: pm@bio.aau.dk
AF: Department of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, sohngaardsholmsvej 57, Aalborg, DK-9000, Denmark
AU: Komatsu, T
EM: komatsu@post.saitama-u.ac.jp
AF: Department of Civil & Environmental Engineering, Graduate School of Science & Engineering, Saitama University, 255 Shimo-Okubo, Saitama, 338-8570, Japan
AB: The transport and fate of gases in soils is mainly governed by gas diffusion and advection. The gas diffusivity (Dp/D₀) is the transport parameter for the gas diffusion due to gas concentration gradient, while the air permeability (k_a) is the transport parameter for advective gas transport due to soil-air pressure gradient. Hence, those gas transport parameters play a crucial role in simulating transport of gaseous contaminants such as volatile organic chemicals and in quantifying emission and exchange of greenhouse gases from/at the soil- atmosphere interface. In this study, we measured Dp/D₀ and k_a for total of six sandy soils and examined the effects of soil physical properties such as particle size, soil compaction, and sample scale on the gas transport parameters. Toyoura sand (0.106-0.50 mm) and Narita sands with three different particle size fractions (0.106-0.25, 0.25- 0.425, 0.425-0.85 mm) were used as experimental materials for the measurements of Dp/D₀ and k_a. The sand materials were repacked with given bulk densities into small-scale cores of 100 cm³ (for all materials) and large-scale cores of 2120 cm³ (only for Toyoura sand) at given water contents. In addition to the measurements, Dp/D₀ and k_a of Oso Flaco fine sand and Oakley sand from literature were also analyzed in this study. For all sand materials, we observed the threshold soil-air content (ε_th) below which Dp/D₀ and k_a are negligible, and measured Dp/D₀ and k_a increased linearly with increasing air-filled porosity (ε) from ε_th to soil total porosity (Φ). At high ε, sand materials with larger average particle diameter (APD) gave higher Dp/D₀ and k_a than those with smaller APD sands at a given ε due to the existence of rapid air flow through the highly continuous large pores. At low ε near the ε_th however, the measured Dp/D₀ for large APD sands were lower than those for small APD sands. The measurements for Narita sand fractions with different bulk densities indicated that soil compaction gave the small effects of water blocking for gas diffusion (high Dp/D₀) and the reduction of highly continuous large pores (low k_a). The measured Dp/D₀ and k_a for Toyoura sand with two different soil cores exhibited that no significant scale effect was seen in Dp/D₀, while the measured k_a for large scale were lower than those for small scale cores. Based on the measurements of Dp/D₀ and k_a, we developed new predictive Dp(ε)/D₀ and k_a(ε) models considering ε_th and pore connectivity factor as functions of APD and bulk density for sandy materials. The new models agreed well with the measured Dp/D₀ and k_a and were useful for examining the effects of particle size and soil compaction in sandy soils.
DE: 1865 Soils (0486)
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: 2007 Fall Meeting